another thing that i found to be ''key'' in this process of ''enlarging'' our pectoral size, is dips, but this time going for an extra stretch, i read an article about this bodybuilder who does it this way, and while most people warn against going deep and getting a deep stretch, i've noticed Arnold did his dips pretty deep and the results speak for themselves. Go to the dipping bars, get set up, and then lower yourself slowly first in a controlled manner, and relax, and try to go as deep as you can, without going too deep, if that makes any sense. You see, there's a point where it could be too deep and dangerous, and a lot of times it has to do with your flexibility. at the bottom position, pause for a second, then boom, explode back up, then lower yourself again, and just repeat the process until failure. You might only get 5 or 6 reps like these, and this is fine, helps the chest get stretched out and grow, works like a charm (always consult physician before starting and training program, follow my advice at your own risk)